MENDEL AND THE GENE IDEA

1. MENDEL AND THE GENE IDEA

2. YOU MUST KNOW… • TERMS ASSOCIATED WITH GENETICS PROBLEMS: P, F1, F2, DOMINANT, RECESSIVE, HOMOZYGOUS, HETEROZYGOUS, PHENOTYPIC, AND GENOTYPIC • HOW TO DERIVE THE PROPER GAMETES WHEN WORKING A GENETIC PROBLEM • THE DIFFERENCE BETWEEN AN ALLELE AND A GENE • HOW TO READ A PEDIGREE

3. CONCEPT 14.1 • MENDEL USED THE SCIENTIFIC APPROACH TO IDENTIFY TWO LAWS OF INHERIANCE • P (PARENT) GENERATION – TRUE-BREEDING PARENTS • F1 (FIRST FILIAL) GENERATION – OFFSPRING • F2 (SECOND FILIAL) GENERATION – A CROSS OF THE F1 GENERATION

4. 3:1 INHERITANCE OF F2 OFFSPRING • 4 RELATED CONCEPTS • ALTERNATIVE VERSIONS OF GENES CAUSE VARIATION IN INHERITED CHARACTERISTICS AMONG OFFSPRING (ALLELES THAT ARE THE RESULT OF SLIGHTLY DIFFERENT DNA SEQUENCES) • FOR EACH CHARACTER, EVERY ORGANISM INHERIT ONE ALLELE FROM EACH PARENT

5. 3:1 INHERITANCE OF F2 OFFSPRING • IF THE TWO ALLELES ARE DIFFERENT, THEN THE DOMINANT ALLELE WILL BE FULLY EXPRESSED IN THE OFFSPRING, WHEREAS RECESSIVE ALLELE WILL HAVE NO NOTICEABLE EFFECT ON THE OFFSPRING (LAW OF DOMINANCE) • THE 2 ALLELES FOR EACH CHARACTER SEPARATE DURING GAMETE PRODUCTION (LAW OF SEGREGATION)

6. LAW OF INDEPENDENT ASSORTMENT • MENDEL’S SECOND LAW • EACH PAIR OF ALLELES WILL SEGREGATE INDEPENDENTLY DURING GAMETE FORMATION

7. HOMOZYGOUS – 2 SAME ALLELES (HOMOZYGOUS DOMINANT TT OR HOMOZYGOUS RECESSIVE tt) • HETEROZYGOUS – 2 DIFFERENT ALLELES FOR A TRAIT (Tt) • PHENOTYPE – PHYSICAL EXRESSION OF A TRAIT • GENOTYPE – ORGANISM’S GENETIC MAKEUP

8. TESTCROSS • TO DETERMINE IF THE ORGANISM IS HOMOZYGOUS DOMINANT OR HETEROZYGOUS • TESTCROSS WITH A RECESSIVE ORGANISM

9. MONOHYBRID CROSS INVOLVES THE STUDY OF ONLY ONE CHARACTERISTIC • DIHYBRID CROSS STUDIES TWO CHARACTERISTICS • CROSSING HETEROZYGOUS CHARACTERISTICS YIELDS 9:3:3:1 RESULTS IN A DIHYBRID CROSS

11. CONCEPT 14.2 • THE LAWS OF PROBABILITY GOVERN MENDELIAN INHERITANCE

12. THE RULE OF MULTIPLICATION – WHEN CALCULATING THE PROBABILITY THAT 2 OR MORE INDEPENDENT EVENTS WILL OCCUR TOGETHER IN A SPECIFIC COMBINATION, MULTIPLY THE PROBABILITIES OF EACH OF THE TWO EVENTS • EX. THE PROBABILITY OF A COIN LANDING FACE UP TWO TIMES IN TWO FLIPS IS ½ x ½ = ¼

13. IF YOU CROSS 2 ORGANISMS WITH THE GENOTYPES AABbCc AND AaBbCc, THE PROBABILITY OF AN OFFSPRING HAVING THE GENOTYPE AaBbcc IS ½ x ½ x ¼ = 1/16

14. THE RULE OF ADDITION – WHEN CALCULATING THE PROBABILITY THAT ANY OF 2 OR MORE MUTUALLY EXCLUSIVE EVENTS WILL OCCUR, YOU NEED TO ADD TOGETHER THEIR INDIVIDUAL PROBABILITIES • EX. IF YOU ARE TOSSING A DIE, WHAT IS THE PROBABILITY THAT IT WILL LAND ON EITHER THE SIDE WITH 4 SPOTS OR THE SIDE WITH 5 SPOTS? • 1/6 + 1/6 = 1/3

15. CONCEPT 14.3 • INHERITANCE PATTERNS ARE OFTEN MORE COMPLEX THAN PREDICTED BY SIMPLE MENDELIAN GENETICS

16. COMPLETE DOMINANCE – THE HETEROZYGOTE AND THE HOMOZYGOTE FOR THE DOMINANT ALLELE ARE INDISTINGUISHABLE • Yy AND YY ARE BOTH YELLOW • CODOMINANCE – OCCURS WHEN TWO ALLELES ARE DOMINANT AND AFFECT THE PHENOTYPE IN TWO DIFFERENT BUT EQUAL WAYS • EX. AB BLOOD TYPE, SPOTTED CHICKEN

18. INCOMPLETE DOMINANCE – THE F1 HYBRIDS HAVE AN APPEARANCE THAT IS IN BETWEEN THAT OF THE TWO PARENTS • RED FLOWERS CROSSED WITH WHITE FLOWERS PRODUCES PINK FLOWERS • MULTIPLE ALLELES – OCCURS WHEN A GENE HAS MORE THAN TWO ALLELES • EX. BLOOD TYPES

20. PLEIOTROPY – PROPERTY OF A GENE THAT CAUSES IT TO HAVE MULTIPLE PHENOTYPIC EFFECTS • EX. SICKLE-CELL DISEASE HAS MULTIPLE SYPTOMS ALL DUE TO A SINGLE DEFECTIVE GENE • EPISTASIS – A GENE AT ONE LOCUS ALTERS THE EFFECTS OF A GENE AT ANOTHER LOCUS • EX. AN INDIVIDUAL MAY HAVE GENES FOR HEAVY SKIN PIGMENTATION BUT IF A SEPARATE GENE THAT PRODUCES THE PIGMENT IS DEFECTIVE, THE GENES FOR PIGMENT DEPOSITION WILL NOT BE EXPRESSED AND CAUSE ALBINISM

21. POLYGENIC INHERITANCE – TWO OR MORE GENES HAVE AN ADDITIVE EFFECT ON A SINGLE CHARACTER IN THE PHENOTYPE • EX. HEIGHT, SKIN COLOR

22. CONCEPT 14.4 • MANY HUMAN TRAITS FOLLOW MENDELIAN PATTERNS OF INHERITANCE

23. PEDIGREE • DIAGRAM SHOWING THE RELATIONSHIP BETWEEN PARENTS AND OFFSPRING ACROSS TWO OR MORE GENERATIONS • PEDIGREES CAN HELP DETERMINE THE GENOME OF INDIVIDUALS THAT COMPRISE THEM • CAN HELP PREDICT THE GENOME OF FUTURE OFFSPRING

25. RECESSIVELY INHERITED DISORDERS • REQUIRE TWO COPIES OF THE DEFECTIVE GENE FOR THE DISORDER TO BE EXPRESSED

26. CYSTIC FIBROSIS • CAUSED BY A MUTATION IN AN ALLELE THAT CODES FOR A CELL MEMBRANE PROTEIN THAT FUNCTIONS IN THE TRANSPORT OF CHLORIDE IONS INTO AND OUT OF CELL • THE HIGH EXTRACELLULAR LEVELS OF CHLORIDE CAUSE THICK MUCUS

28. TAY-SACHS • CAUSED BY AN ALLELE THAT CODES FOR A DYSFUNCTIONAL ENZYME THAT IS UNABLE TO BREAK DOWN CERTAIN LIPIDS IN THE BRAIN • LIPIDS ACCUMULATE IN THE BRAIN CELLS CAUSING BLINDNESS, SEIZURES, DEGENERATION OF BRAIN FUNCTION, DEATH

29. SICKLE-CELL DISEASE • CAUSED BY AN ALLELE THAT CODES FOR A MUTANT HEMOGLOBIN MOLECULES THAT FORMS LONG RODS WHEN THE OXYGEN LEVELS IN THE BLOOD ARE LOW • RBC CLOG SMALL BLOOD VESSELS LEADING TO PAIN AND ORGAN DAMAGE

30. LETHAL DOMINANT ALLELES – REQUIRE ONLY ONE COPY OF THE ALLELE IN ORDER FOR THE DISORDER TO BE EXPRESSED • HUNTINGTON’S DISEASE – CAUSED BY A LETHAL DOMINANT ALLELE • DEGENERATION OF THE NERVOUS SYSTEM

31. GENETIC TESTING • AMNIOCENTESIS – REMOVAL OF AMNIOTIC FLUID FROM AROUND THE FETUS • CHORIONIC VILLUS SAMPLING – A TINY SAMPLE OF THE PLACENTA THAT CONTAINS ONLY FETAL CELLS IS SUCTIONED OUT THROUGH THE CERVIX • KARYOTYPING IS PERFORMED